Development of an empirical correlation for the onset of flow instability in narrow rectangular channels

An empirical correlation has been developed to accurately predict the onset of flow instability (OFI) in narrow rectangular channels under a wide thermal–hydraulic condition. The 242 sets of OFI experiments were collected, which cover a wide range of thermal–hydraulic conditions with pressures ranging from 0.103 to 1.73 MPa, a heat flux ranging from 0.1 to 16.8 MW/m², a mass flux ranging from 151 to 20,325 kg/m²·s, Pe ranging from 6650 to 358,460, and Pr ranging from 0.94 to 3.17. The test sections have gap sizes between 1.27 and 3.6 mm, hydraulic diameters between 2.37 and 6.58 mm, and a length-to-heated diameter ratio between 82.3 and 197.5. The collected experimental data were analyzed to find out the effects of parameters on the OFI. From the analysis, non-dimensional numbers affecting the OFI point were determined and an empirical correlation was developed. The new empirical correlation as well as several existing net vapor generation (NVG) and OFI correlations were assessed against the OFI experimental data. It was shown that the proposed correlation provides agreements with the experimental OFI points than the other correlations.